I finally got reading the Subversion authz file working (at least the basic UI layout). This screenshot is done against one of my live Subversion servers:

So my next step is reading the actual path permission in code, then figuring out how to do an UI for that. The "kernel" that drives PainlessSVN is actually open sourced and it's called SVNManagerLib. I'm hosting it over at CodePlex. Writing this code is not that hard compared to all the UI tricks that I need to use to present this to users.